Most patients often respond to this treatment at first but are at a high-risk for the cancer coming back. The majority of the children who relapse after treatment or develop recurrent disease do so in the first two years following the completion of therapy and there are no current treatments to cure those who relapse. This study will explore whether or not extending the therapy with isotretinoin from 6 months to 24 months will help prevent the cancer from coming back without causing severe side effects.